i) Technical Field of the Invention
This invention relates to a control device of a motor, which estimates an operating state of a control target using a state estimator (observer), for example, and controls the motor by a feedback control based on the estimation.
ii) Description of the Related Art
Heretofore, an image forming apparatus, such as a printer and a facsimile, has been provided with a conveying device that conveys a sheet fed by a feeding device, as an image forming by an image forming unit, like a record head, onto the sheet proceeds. This type of conveying device comprises a conveying roller that is brought into frictional contact with the sheet to convey the same, and a driving source, such as a motor, that rotationally drives the conveying roller. The conveying device regulates a rotation amount of the conveying roller according to operating instructions to convey the sheet from the outside. As the sheet is conveyed by the conveying roller, an image is recorded onto the sheet by the image forming unit.
Conventionally, the driving source that rotationally drives the conveying roller in such a conveying device has been a stepping motor. However, the stepping motor rotates itself by a predetermined step angle according to a received pulse signal. Therefore, it is difficult to pursue both high speeding and high resolution. Furthermore, due to its specific operational characteristics, it has been very difficult to reduce noise during the operation.
These days, owing to an increase in demands for high speeding, high resolution, as well as silence, in the image forming apparatus, a DC motor becomes dominant as the driving source that rotationally drives the conveying roller. For example, the DC motor is used as a feeding motor and a carriage motor in an ink jet printer.
Japanese Patent Publication No. 2003-23783 discloses an ink jet printer which performs switching of a gain according to a driving load of a DC motor at the time of feedback controlling the DC motor. Thereby, a time period required for the DC motor to reach a predetermined rotation velocity becomes constant regardless of a magnitude of the driving load of the DC motor.